Lookout Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lookout Observatory clear sky chart from 2005-11-06 to 2024-12-09.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	14% 7% 2 6% 5% 4 5% 4 6% 7% 40%	101200
	Night	14% 6% 2 6% 4 4 4 3 5% 7% 44%	98556
Transparency	Day	40% 6% 11% 21% 18% 5%	105006
	Night	38% 5% 10% 22% 20% 6%	102888
Seeing	Day	19% 11% 23% 23% 17% 8%	14789
	Night	17% 9% 22% 29% 20% 4	24812

By Month

Percentage Cloud Cover SE (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	18% 12% 4 5% 4 3 4 4 5% 5% 36%	2836
	11th to 20th	Day	19% 7% 3 7% 4 3 3 2 3 4 43%	2840
	21st to end	Day	25% 9% 2 5% 2 2 3 3 3 5% 40%	3377
February	1st to 10th	Day	18% 10% 3 6% 4 4 4 3 4 6% 38%	1900
	11th to 20th	Day	23% 8% 2 6% 5% 4 4 3 4 4 38%	1848
	21st to end	Day	22% 8% 2 6% 5% 4 4 3 4 4 38%	1570
March	1st to 10th	Day	25% 10% 3 6% 4 4 4 4 6% 5% 30%	3120
	11th to 20th	Day	16% 7% 2 6% 4 4 4 2 4 6% 46%	3446
	21st to end	Day	16% 7% 3 7% 5% 4 4 4 6% 7% 37%	3815
April	1st to 10th	Day	13% 7% 2 5% 5% 4 5% 4 6% 7% 43%	2277
	11th to 20th	Day	14% 6% 2 6% 5% 4 4 3 5% 6% 45%	2254
	21st to end	Day	11% 4 2 6% 5% 4 5% 4 6% 8% 46%	2361
May	1st to 10th	Day	12% 7% 2 6% 5% 4 5% 4 6% 7% 42%	4082
	11th to 20th	Day	17% 7% 3 6% 5% 4 5% 4 6% 8% 36%	4081
	21st to end	Day	10% 6% 3 6% 4 5% 5% 4 7% 9% 42%	4476
June	1st to 10th	Day	11% 7% 2 7% 6% 5% 6% 5% 7% 9% 34%	2470
	11th to 20th	Day	4 5% 2 6% 6% 5% 5% 6% 8% 11% 41%	2470
	21st to end	Day	8% 5% 2 7% 6% 5% 7% 5% 8% 10% 38%	2470
July	1st to 10th	Day	9% 6% 3 8% 6% 7% 7% 6% 9% 11% 29%	4120
	11th to 20th	Day	9% 5% 3 7% 6% 7% 7% 6% 8% 10% 31%	4120
	21st to end	Day	14% 11% 4 11% 8% 7% 6% 5% 7% 9% 19%	4466
August	1st to 10th	Day	5% 3 2 4 5% 5% 6% 5% 9% 11% 45%	3986
	11th to 20th	Day	7% 4 2 6% 5% 5% 6% 6% 9% 11% 40%	3729
	21st to end	Day	9% 4 2 5% 4 5% 5% 4 6% 7% 48%	4180
September	1st to 10th	Day	11% 7% 2 7% 5% 6% 5% 4 7% 9% 37%	2174
	11th to 20th	Day	17% 5% 2 6% 4 5% 5% 3 5% 7% 39%	2090
	21st to end	Day	15% 5% 2 6% 4 3 3 3 5% 6% 47%	2090
October	1st to 10th	Day	12% 5% 2 5% 3 4 4 3 4 5% 53%	2090
	11th to 20th	Day	10% 5% 2 6% 3 3 3 3 5% 5% 55%	2055
	21st to end	Day	14% 5% 2 4 3 4 3 3 4 5% 53%	1986
November	1st to 10th	Day	13% 6% 2 4 4 3 3 3 4 6% 52%	1762
	11th to 20th	Day	14% 5% 2 5% 4 3 4 4 5% 6% 49%	1800
	21st to end	Day	17% 7% 2 5% 4 3 4 3 5% 6% 46%	1800
December	1st to 10th	Day	21% 8% 2 6% 4 4 4 3 4 5% 38%	1782
	11th to 20th	Day	17% 8% 3 7% 4 4 4 3 4 5% 41%	2153
	21st to end	Day	20% 9% 4 7% 4 4 4 3 5% 7% 34%	3124
January	1st to 10th	Night	18% 10% 3 6% 3 4 3 3 5% 5% 40%	4109
	11th to 20th	Night	18% 7% 3 6% 4 3 3 3 4 5% 43%	4120
	21st to end	Night	24% 12% 2 5% 3 4 3 2 4 4 38%	4276
February	1st to 10th	Night	17% 7% 3 6% 4 4 4 3 5% 6% 43%	2280
	11th to 20th	Night	21% 7% 2 7% 4 5% 4 2 4 5% 40%	2218
	21st to end	Night	21% 8% 3 7% 4 4 5% 3 5% 5% 36%	1884
March	1st to 10th	Night	27% 10% 3 6% 4 3 3 3 4 5% 32%	3733
	11th to 20th	Night	11% 6% 2 6% 4 4 4 3 6% 7% 48%	3513
	21st to end	Night	15% 9% 3 7% 5% 4 4 4 5% 5% 40%	3817
April	1st to 10th	Night	12% 5% 1 5% 4 4 4 4 6% 7% 48%	1917
	11th to 20th	Night	14% 5% 2 5% 3 4 3 3 5% 6% 50%	1875
	21st to end	Night	10% 5% 2 5% 4 3 4 4 6% 7% 51%	1819
May	1st to 10th	Night	12% 7% 3 7% 5% 4 4 4 6% 7% 41%	2813
	11th to 20th	Night	16% 6% 2 6% 4 3 5% 4 7% 9% 38%	2812
	21st to end	Night	7% 5% 2 6% 4 4 5% 5% 6% 11% 44%	3079
June	1st to 10th	Night	7% 6% 3 7% 5% 6% 5% 5% 7% 10% 40%	1710
	11th to 20th	Night	5% 4 2 4 4 3 4 4 8% 11% 52%	1710
	21st to end	Night	5% 5% 2 5% 5% 4 5% 5% 8% 12% 44%	1710
July	1st to 10th	Night	8% 6% 3 7% 5% 6% 6% 5% 8% 11% 34%	2840
	11th to 20th	Night	8% 5% 2 5% 5% 4 5% 5% 8% 12% 41%	2840
	21st to end	Night	12% 9% 4 9% 6% 6% 6% 5% 7% 10% 26%	3087
August	1st to 10th	Night	5% 3 2 4 4 4 5% 4 8% 11% 50%	2939
	11th to 20th	Night	8% 4 2 5% 3 4 4 3 6% 9% 51%	3100
	21st to end	Night	8% 3 2 4 3 3 4 3 6% 8% 56%	3476
September	1st to 10th	Night	9% 6% 3 5% 4 5% 5% 4 7% 9% 43%	1985
	11th to 20th	Night	14% 6% 2 7% 4 4 4 4 5% 9% 42%	2090
	21st to end	Night	12% 5% 1 5% 3 3 4 3 5% 7% 52%	2090
October	1st to 10th	Night	11% 4 2 5% 3 2 3 3 4 5% 59%	2090
	11th to 20th	Night	12% 5% 2 4 4 4 3 2 4 5% 55%	2123
	21st to end	Night	13% 5% 1 5% 3 3 3 3 4 5% 55%	2610
November	1st to 10th	Night	14% 5% 2 4 4 3 3 3 5% 6% 52%	2536
	11th to 20th	Night	14% 6% 1 4 3 3 3 3 5% 6% 52%	2600
	21st to end	Night	16% 7% 2 5% 4 3 4 4 5% 6% 46%	2600
December	1st to 10th	Night	20% 6% 3 7% 5% 3 3 3 4 6% 38%	2581
	11th to 20th	Night	17% 7% 2 5% 4 3 3 3 4 5% 47%	3042
	21st to end	Night	20% 7% 3 7% 4 4 5% 4 7% 8% 32%	4532

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	49% 3 6% 17% 22% 3	2837
	11th to 20th	Day	45% 3 6% 19% 25% 2	2840
	21st to end	Day	48% 3 6% 20% 20% 4	3377
February	1st to 10th	Day	47% 3 7% 20% 20% 3	1900
	11th to 20th	Day	50% 3 4 20% 18% 5%	1858
	21st to end	Day	50% 3 6% 16% 20% 5%	1570
March	1st to 10th	Day	54% 3 9% 11% 14% 8%	3120
	11th to 20th	Day	41% 3 6% 22% 21% 7%	3446
	21st to end	Day	45% 4 11% 21% 15% 3	3815
April	1st to 10th	Day	39% 5% 10% 22% 19% 5%	2277
	11th to 20th	Day	40% 4 6% 20% 23% 6%	2254
	21st to end	Day	35% 4 11% 30% 17% 3	2361
May	1st to 10th	Day	40% 5% 13% 25% 14% 2	4120
	11th to 20th	Day	45% 5% 13% 26% 11% 1	4085
	21st to end	Day	38% 5% 11% 25% 19% 1	4489
June	1st to 10th	Day	43% 7% 15% 22% 12% 1	2470
	11th to 20th	Day	32% 8% 18% 26% 14% 2	2470
	21st to end	Day	37% 8% 18% 22% 12% 3	2470
July	1st to 10th	Day	42% 12% 21% 18% 7% 1	4055
	11th to 20th	Day	41% 12% 21% 19% 6% 1	4051
	21st to end	Day	58% 9% 14% 14% 5%	4324
August	1st to 10th	Day	27% 8% 16% 37% 12% 1	3973
	11th to 20th	Day	32% 9% 17% 26% 13% 2	3765
	21st to end	Day	31% 8% 13% 24% 21% 3	4179
September	1st to 10th	Day	41% 8% 14% 16% 15% 6%	2174
	11th to 20th	Day	43% 6% 10% 21% 18% 2	2090
	21st to end	Day	37% 5% 11% 20% 20% 8%	2090
October	1st to 10th	Day	24% 4 6% 15% 38% 14%	3480
	11th to 20th	Day	22% 3 5% 19% 29% 23%	3399
	21st to end	Day	27% 5% 6% 23% 28% 12%	3249
November	1st to 10th	Day	35% 3 5% 19% 29% 9%	1762
	11th to 20th	Day	35% 4 6% 20% 26% 9%	1800
	21st to end	Day	39% 4 6% 21% 25% 5%	1800
December	1st to 10th	Day	48% 4 6% 18% 20% 4	1782
	11th to 20th	Day	45% 3 5% 18% 23% 5%	2150
	21st to end	Day	50% 4 8% 19% 16% 3	3124
January	1st to 10th	Night	47% 3 4 19% 24% 4	4109
	11th to 20th	Night	43% 3 6% 21% 18% 8%	4120
	21st to end	Night	51% 2 4 16% 22% 5%	4276
February	1st to 10th	Night	43% 3 7% 20% 21% 5%	2280
	11th to 20th	Night	48% 3 6% 19% 17% 7%	2219
	21st to end	Night	50% 4 6% 16% 18% 7%	1884
March	1st to 10th	Night	56% 3 7% 13% 16% 6%	3733
	11th to 20th	Night	35% 4 8% 21% 22% 10%	3513
	21st to end	Night	46% 4 7% 21% 19% 3	3817
April	1st to 10th	Night	34% 4 12% 22% 22% 5%	1917
	11th to 20th	Night	36% 3 6% 23% 21% 10%	1875
	21st to end	Night	32% 5% 10% 30% 20% 4	1819
May	1st to 10th	Night	42% 4 14% 23% 16% 2	2840
	11th to 20th	Night	42% 5% 15% 26% 11% 1	2813
	21st to end	Night	32% 5% 15% 28% 17% 2	3087
June	1st to 10th	Night	39% 6% 17% 22% 15% 2	1710
	11th to 20th	Night	24% 6% 22% 28% 17% 2	1710
	21st to end	Night	31% 6% 20% 23% 15% 5%	1710
July	1st to 10th	Night	39% 11% 21% 21% 7% 1	2795
	11th to 20th	Night	32% 8% 26% 24% 7% 2	2786
	21st to end	Night	51% 11% 15% 16% 6% 1	2988
August	1st to 10th	Night	24% 7% 17% 38% 12% 1	2928
	11th to 20th	Night	29% 6% 19% 28% 16% 1	3130
	21st to end	Night	25% 7% 15% 22% 28% 3	3476
September	1st to 10th	Night	36% 6% 17% 20% 15% 5%	1985
	11th to 20th	Night	39% 7% 13% 20% 20% 2	2090
	21st to end	Night	33% 4 10% 23% 22% 7%	2090
October	1st to 10th	Night	20% 5% 7% 18% 33% 17%	3480
	11th to 20th	Night	20% 2 4 18% 33% 23%	3518
	21st to end	Night	24% 3 5% 26% 30% 12%	4297
November	1st to 10th	Night	34% 4 8% 20% 24% 11%	2536
	11th to 20th	Night	33% 3 5% 21% 27% 10%	2600
	21st to end	Night	39% 4 5% 23% 23% 7%	2600
December	1st to 10th	Night	46% 4 8% 18% 20% 4	2581
	11th to 20th	Night	40% 4 6% 18% 28% 4	3044
	21st to end	Night	48% 4 7% 21% 18% 2	4532

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	33% 22% 32% 13% 1	270
	11th to 20th	Day	37% 17% 31% 11% 3 1	270
	21st to end	Day	26% 26% 33% 13% 2	297
February	1st to 10th	Day	33% 19% 33% 12% 3	270
	11th to 20th	Day	40% 25% 26% 8% 1	270
	21st to end	Day	41% 19% 36% 3 1	225
March	1st to 10th	Day	31% 17% 34% 14% 3 1	270
	11th to 20th	Day	25% 21% 31% 18% 5% 1	439
	21st to end	Day	22% 17% 37% 17% 6%	506
April	1st to 10th	Day	25% 15% 29% 18% 12% 2	460
	11th to 20th	Day	19% 16% 31% 22% 10% 1	452
	21st to end	Day	18% 14% 32% 20% 13% 3	460
May	1st to 10th	Day	16% 13% 30% 24% 12% 5%	463
	11th to 20th	Day	15% 6% 23% 31% 14% 11%	487
	21st to end	Day	15% 6% 18% 27% 22% 13%	529
June	1st to 10th	Day	16% 5% 19% 30% 18% 13%	490
	11th to 20th	Day	7% 4 15% 29% 25% 20%	490
	21st to end	Day	11% 4 19% 28% 22% 17%	490
July	1st to 10th	Day	12% 3 11% 25% 29% 20%	485
	11th to 20th	Day	10% 3 11% 23% 32% 21%	484
	21st to end	Day	9% 3 9% 27% 30% 22%	532
August	1st to 10th	Day	14% 3 12% 25% 28% 20%	486
	11th to 20th	Day	13% 3 12% 33% 27% 12%	479
	21st to end	Day	16% 4 7% 26% 31% 16%	539
September	1st to 10th	Day	10% 4 14% 30% 28% 12%	490
	11th to 20th	Day	19% 4 13% 23% 31% 9%	490
	21st to end	Day	17% 6% 17% 27% 27% 6%	490
October	1st to 10th	Day	14% 5% 23% 28% 22% 7%	490
	11th to 20th	Day	14% 11% 27% 29% 18% 2	490
	21st to end	Day	19% 11% 26% 27% 15% 2	435
November	1st to 10th	Day	22% 14% 30% 24% 8% 2	300
	11th to 20th	Day	19% 19% 37% 21% 4	300
	21st to end	Day	20% 21% 33% 19% 6% 2	300
December	1st to 10th	Day	30% 18% 38% 11% 2 1	294
	11th to 20th	Day	26% 20% 33% 16% 6%	270
	21st to end	Day	32% 15% 35% 13% 4 1	297
January	1st to 10th	Night	25% 17% 31% 23% 4	760
	11th to 20th	Night	23% 17% 29% 24% 6%	760
	21st to end	Night	22% 17% 36% 23% 3	836
February	1st to 10th	Night	21% 14% 32% 29% 4	760
	11th to 20th	Night	25% 18% 32% 23% 2	743
	21st to end	Night	27% 18% 32% 20% 3	628
March	1st to 10th	Night	20% 15% 31% 29% 5%	760
	11th to 20th	Night	19% 15% 31% 25% 8% 1	760
	21st to end	Night	20% 14% 29% 28% 10%	836
April	1st to 10th	Night	14% 15% 28% 31% 11% 1	587
	11th to 20th	Night	16% 11% 30% 29% 12% 2	563
	21st to end	Night	12% 9% 23% 38% 17% 1	570
May	1st to 10th	Night	11% 7% 26% 32% 22% 2	570
	11th to 20th	Night	13% 5% 19% 35% 21% 6%	561
	21st to end	Night	12% 2 11% 32% 37% 5%	617
June	1st to 10th	Night	9% 2 12% 36% 35% 5%	570
	11th to 20th	Night	5% 1 11% 32% 38% 12%	570
	21st to end	Night	7% 2 9% 31% 41% 10%	570
July	1st to 10th	Night	9% 3 7% 23% 43% 15%	555
	11th to 20th	Night	9% 2 6% 24% 45% 15%	552
	21st to end	Night	9% 2 7% 26% 46% 10%	624
August	1st to 10th	Night	7% 2 6% 25% 47% 14%	567
	11th to 20th	Night	13% 4 8% 29% 38% 8%	564
	21st to end	Night	14% 3 6% 26% 42% 8%	627
September	1st to 10th	Night	10% 3 10% 31% 36% 9%	655
	11th to 20th	Night	16% 3 11% 28% 37% 5%	760
	21st to end	Night	14% 3 15% 29% 34% 4	760
October	1st to 10th	Night	12% 4 21% 33% 25% 6%	760
	11th to 20th	Night	15% 7% 23% 32% 20% 2	760
	21st to end	Night	15% 8% 20% 37% 17% 3	836
November	1st to 10th	Night	16% 8% 23% 32% 18% 3	780
	11th to 20th	Night	16% 12% 29% 30% 11% 1	800
	21st to end	Night	21% 10% 26% 31% 11% 1	800
December	1st to 10th	Night	25% 13% 27% 28% 7% 1	795
	11th to 20th	Night	24% 12% 28% 28% 8%	760
	21st to end	Night	27% 13% 24% 29% 6%	836

Page generated at 2024-12-06 02:54:49. Version ac07

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